The present invention relates to polymeric coatings which comprise reaction products of polyvinyl alcohol (PVA) which are insoluble in boiling water and subsequently complexed with iodine and/or borates that exhibit antiseptic, broad-spectrum antimicrobial activity in a controlled and sustained manner. More specifically, the present invention relates to a method of rendering a polyvinyl alcohol substrate coating insoluble in boiling water by using non-mineral acid catalysts and specific curing agents.
Disinfectants can be defined as chemical agents that kill pathogenic organisms. Disinfection is directed against fungi, viruses, bacteria and eukaryotic parasites, such as Giarda. Traditional disinfectants act in dilute solutions by diverse mechanisms, to kill microorganisms, but can leave potentially contaminating residues behind. When applied to animate surfaces, some disinfectants may be undesirable because they also can leave rather high residual concentrations behind on the wound surface, which can adversely affect surrounding healthy tissue. Iodine is an example of a very effective disinfectant which is active in parts per million, but damaging to healthy tissue in larger amounts. In the liquid forms currently commercially available, the amount of iodine administered cannot be controlled. Other typical disinfectants include sodium hypochlorite/Chlorox, aqueous and alcoholic iodine, povidone iodine, aqueous silver nitrate, hydrogen peroxide, phenol, alcohols, benzalkonium chloride, etc.
Solid phase disinfectants are known as xe2x80x9ccontactxe2x80x9d antimicrobials that require that the pathogenic microorganisms contact a biocidal surface, which then release an antimicrobial agent. Some solid phase disinfectants release this toxic dose of disinfectant to microorganisms upon contact, leaving very little extra or residual disinfectant behind in the absence of any microorganisms. These are called demand solid phase contact release disinfectants. Iodine, in certain complexed forms, can be such a disinfectant, and, in addition, even have some capability to differentiate between the proteinaceous matter of bacteria and the proteins present in surrounding healthy tissue. This PVA/iodine starch complex will therefore lose less specificity or effectiveness against the bacteria. Most disinfectants are soon rendered ineffective, since they are reactive toward diluting body fluids and tissue. Well known, demand release type disinfectants include strong base anion exchange resins described in U.S. Pat. No. 5,431,908, and other U.S. Pat. Nos. 3,817,860 and 3,923,665, describing other types of ion exchange resins that bind or complex iodine for use in water treatment disinfection. Insolubilized PVA/iodine complexes, even though not an ion exchange resin also releases small, controlled amounts of iodine (U.S. Pat. No. 5,071,648), which performs as a solid phase antimicrobial on contact, and can also be formed into a useful coating.
U.S. Pat. No. 5,071,648, discloses a post treatment insolubilizing process for forming a free standing film. However, insolubilizing the free standing film requires its post immersion in a solution of formaldehyde and sulphuric acid to cause the acetal cure and insolubility. U.S. Pat. No. 5,071,648 also discloses effective antimicrobial polyvinyl acetal sponge wipes. However, they are generally too costly for most applications because they are based in its entirety on one expensive material (PVA sponge) and also because of this limitation, cannot form the various shapes and combinations necessary to fulfill many industrial and consumer needs.
U.S. Pat. No. 5,071,648 also discloses another free standing film forming process for forming highly insoluble films, which resin solution also contains formaldehyde and sulphuric acid to form insoluble acetals. It further describes a coating of a matrix reinforcement which is sized with pure PVA, without a curing agent, to be subsequently complexed with iodine. However, these sizing coatings are not highly insolubilized, nor do they have to be, as they are proposed for use in non-wiping applications, e.g., to create a single use antiseptic area or environment for application to surgical drapes, gowns and wet dressings, which do not require high coating strength, as would be necessary in a multi-use wiping or scrubbing product.
The prior art in general also teaches coating a PVA foam onto a polyester (Dacron) reinforcing substrate which resin formula also contains mineral acid and formaldehyde curing agents to form acetal cures. These non-iodine complexed PVA foam products are used as car chamois and sport toweling. Polyester is resistant to mineral acid attack, but polyester is limited in the forms available, e.g. no sponges or papers, and the prior art does not describe iodine complexing these polyester reinforced PVA foam sheets.
It is important to note that in order to deposit insolubilized PVA onto a cellulose substrate, previous to iodine complexing, the insolubilizing components of the PVA coating solution must not contain a component that can substantially attack or break down the substrate. Since mineral acid catalysis to form insoluble acetals is the means by which PVA in the prior art is commonly cured, and mineral acids break down cellulose sponges, papers, and cotton cloths, etc., other means by which PVA can be insolubilized are required. In addition, the alternative PVA curing or insolubilizing agents also must not attack cellulose, and must effectively and economically cure the PVA without interfering with the subsequent step of iodine complexing.
The present invention provides a method of making highly insolubilized PVA coatings without the use of mineral acids. Surprisingly, the insolubilizing PVA agents of the present invention not only do not degrade the cellulose substrate but also do not interfere in the iodine complexing reaction, permit a more controllable iodine release with wider applicability at less cost.
It is the object of this invention to provide a method for preparing less expensive, more widely applicable antimicrobial sponges, cloths and papers.
It is also the object of this invention to form highly insoluble PVA non-mineral acid catalyzed coating (not soluble in boiling water) systems for depositing on, and interstitially onto a variety of readily available, inexpensive, e.g. cellulose derived, or other economical substrates without attacking such substrates.
It is a further object of this invention to complex this coating with iodine and/or borates, to produce controlled iodine release coating materials inexpensively, in the form of conventional cellulose sponges, cloths, papers, non-wovens, etc.
It is a further object of this invention to control the amount of iodine content, and its release, by controlling the amount of insolubilized PVA on the substrate to which it is complexed.
It is also another object of this invention to mix PVA with other iodine compounds and/or iodine complexing materials that are also compatible with PVA and/or iodine.
The present invention provides a method for making a substrate normally not capable of being complexed with iodine, said substrate being made capable of iodine complexing, by coating or impregnating the substrate with a solution containing a PVA polymeric mix that can be rendered insoluble by curing in the presence of a non-mineral acid catalysts and optionally a cross-linking agent, and subsequently iodine complexing to act as a solid state antimicrobial device.
The presence of the curing agent (which is defined herewith as the non-mineral catalyst and optionally the cross-linking agent) of the present invention has an insolubilizing effect, yet still permits the formation of post iodine complexes, and most important, has little or no noticeable effect on the mechanical strength of the substrate receiving the coating, and is economical and allows ease of manufacture.
Preferably, the non-mineral acid catalyst is selected from the group consisting of ammonium chloride, ammonium sulfate and magnesium chloride. Also preferably, the cross-linking agent is selected from the group consisting of amine aldehyde, epoxy, polyol amine, metal salt, metal complex, organo metallic, acid salt and organic acid anhydride. Preferable crosslinking agents include: melamine formaldehyde and urea formaldehyde as amine formaldehydes; epoxys as polyamid-epichlorohydrins, trimethylol melamine and dimethylol urea as polyol amines; ammonium dichromate as a metal salt; cupra ammonium hydroxide complex as a metal complex; chrome/fatty acid complex or organic titanate as the organo metallics; and maleic anhydride as the organic acid anhydride.
A substrate such as a cellulose sponge is coated with the PVA/curing agent solution, dried and cured at a temperature of about 125-230xc2x0 F., and its weight noted as to its PVA content. The cured PVA impregnated substrate is washed, if necessary, and is then complexed with an iodine solution containing excess iodine. The sponge is rinsed out to flush out the excess iodine. The weight of the base sponge is subtracted from the cured PVA impregnated sponge, noting its PVA content. Knowing the amount of iodine that complexes with that PVA resin mix under excess iodine conditions, and knowing the weight of the PVA that remained with the sponge, the amount of iodine can be calculated. Thereby, a product can be attained whose iodine content is known and may be specified for each application and market with a designated content of iodine and predictable antimicrobial activity and longevity for the circumstances for which it is intended. If an adjustment in antimicrobial activity is desired, the concentration of the PVA resin mix impregnate can be varied, but still fully complexed with an excess iodine solution. In practice, preparatory experiments will determine the average weight of a group of base sponges that can be assigned to a batch of sponges die cut to the same dimensions, which eliminates weighing each sponge. Also, a designated concentration of PVA resin mix will be chosen that when impregnated and squeezed out under a set pressure and gap between rollers to achieve a practical reproduceability of resin pickup will eliminate the need for weighing each impregnated sponge and thereby rely more on statistical analysis. After iodine complexing, the sponge is rinsed out of surplus iodine, dried or kept moist, and the cured PVA iodine complex will remain as an insoluble coating, even upon numerous re-wettings and uses. Washed out excess iodine can be recovered by running the wash water through ion exchange resins or by other PVA coated substrates.
The prior art (U.S. Pat. No. 5,071,648) describes an iodine complexed polyvinyl acetal sponge, with desirable antimicrobial properties. The sponge is derived from foamed polyvinyl alcohol, which is acetalized to form an open celled, insoluble matrix, which is totally capable of complexing iodine on or throughout its matrix. Since the bulk material of the sponge, and the iodine complexing component of the sponge are the same, the amount or weight of iodine complexed with the sponge is proportional to the total amount of sponge material present when the iodine content of the complexing solution is not limited. Therefore, the amount of iodine complexed and the size or weight of the PVA sponge are dependent on each other, e.g. the larger the sponge, the more iodine will be complexed. Since iodine is a very effective antimicrobial agent, most often only a very small amount of iodine release (parts per million only) is generally necessary to be effective. Since a certain amount of bulk is required for handling or for other mechanical reasons, this complexed sponge in the prior art may therefore contain a much greater amount of iodine than necessary for its intended antimicrobial use. Also, if a PVA sponge that needs to contain only a small amount of iodine is desired, the bulk of that sponge may be too small to physically function well.
It is a purpose of this invention to make the amount of complexed iodine present independent from the mechanical requirements of the sponge or its substrate, which forms its bulk, and therefore the iodine content is more controllable. Also, since the substrate can now be separated from the iodine complexing component, a much wider choice of substrates can now be chosen to better suit the varying types and purposes of applications, e.g. absorption, abrasiveness, type of woven or non-woven matrix, texture, bulk and cost. For example, the amount of iodine and/or borate etc. required to achieve the antimicrobial properties can be specified based on the number of uses and the environment in which it is being used. This information is then combined with the kind of substrate needed to physically fulfill its function in order to come up with a fully specified product. The range of uses include industrial scrubbing and sanitizing a steel table in a meat packing plant with an abrasive backed cellulose PVA/I complexed cellulose sponge to personal sanitizing or wiping with a paper based towelette. It is evident that different iodine content and physical product specifications to fulfill the various needs for each use are necessary. Limiting by dilution the iodine availability to complex with the PVA sponge in the prior art is difficult, as the acetalized PVA polymer is very active toward iodine, and therefore the sponge is quick to disproportionately complex with more iodine at its initial contacting sites, leaving more diluted iodine solutions behind to complex with the remainder of the sponge. It has been observed that diluted iodine solutions, especially at increasingly lower concentrations, as would occur during attempts at lowering iodine content during dilute complexing of the PVA sponge, can form weaker complexes with less homogeneous distribution of the iodine with poorer reproduceable antimicrobial characteristics, that may overall be less effective than fully saturated complexes. Also, since the chemistry of forming iodine complexes with PVA and its derivatives (iodine can exist in various states up to I3 in the presence of iodide ion) is not completely understood, these intermediary or partial complexes also cannot yet be fully predicted. It would therefore be very desirable for ease of manufacture, reliability, quality control, and to maximize antimicrobial effectiveness, to use a controllable amount of PVA in the coating as the means to control iodine content, and keeping the complexing iodine concentration in excess to fully complex the set amount of the PVA coating component, and wash out the excess iodine. Therefore, iodine complexing by saturation, e.g. with excess iodine of the PVA is the preferred method as all the PVA complexing sites are then uniformly satisfied. Thereby, this invention allows for more easily controlling the amount of iodine present, by controlling the amount of PVA coating deposited on and throughout the bulking substrate, and fully iodine complexing the PVA present. Accordingly, the present invention provides the following advantages over the prior art:
1. Cost reduction by allowing for the use of various relatively cheaper types of substrates such as cellulose sponges. Another benefit with the use of a cellulose sponge substrate is that this commercially available household sponge already has an acceptable feel in the consumer""s hand, and better frictional properties when wiped across a surface, e.g. the polyvinyl acetal sponges in the prior art tend to grab and curl under during use. However, by choosing the right substrate, the sponges of this invention can be designed to wipe more smoothly. Also, most other sponges, including open cell commercial polyurethanes, polyvinyl chloride coated urethanes and polyester foams etc. can also be coated and complexed at a fraction of the cost of PVA sponges, and, additionally, are widely available in many grades and shapes.
2. Improvement of the softness and handling properties of the sponge system when dry. Pure PVA sponges, when dry, are very hard and brittle, and more difficult to hydrate to achieve softness before use. Shipping moist PVA sponges increases both packaging and shipping costs. Also, pure PVA sponges must constantly be kept moist both during use and storage. Coated cellulose sponges can be less stiff when dry, more easily wet out, and therefore can be more easily stored dry.
3. Improvement of the wicking or moistening rate of the sponge when dry. Pure dry PVA sponge takes much time to wet out to attain its soft, useful state, while intrinsically more flexible dry cellulose sponges, cloths and papers wet out faster because they wick better due to their cellulose fiber content which increases their wicking rate.
4. Increasing the number of iodine release rate options available, by mixing various other iodine compounds and other complexing materials with the PVA iodine complex, e.g. with polyvinyl pyrolidone and starches. In the prior art, only acetalized PVA sponges are complexed with iodine, limiting its applications.
5. Improvement in controlling the rate, quantity and longevity of release of iodine by varying the curing agent.
6. Simplification of the manufacture, and reducing the cost of treating pollutants produced during the manufacture of acetalized PVA sponge. Acetalized PVA sponge plant effluents contain toxic mineral acids and formaldehyde. The manufacturing processes of this invention, such as the coating of inert substrates such as cellulose matrixes with PVA coatings cured as outlined herein result in effluents which are comparatively much less toxic.
To achieve antimicrobial activity on only one surface of the sponge, or a portion thereof, the present invention provides that a base sponge surface designated to be activated may be dipped into the PVA resin mix solution. The migration of the PVA resin mix solution into the base sponge, can be controlled or limited by using higher viscosity PVA derived from higher PVA resin concentrations, or use of higher molecular weight resins which give increased solution viscosities, or reduce the time the sponge contacts the solution, all of which limit the depth of penetration of the PVA solution into the base sponge.
Another approach to applying the PVA iodine complex over a specific surface or onto an upper portion only, is by spraying the PVA resin mix solution, either with air type spray guns or airless types which spray high viscosity solutions, over the selected surface to be activated, curing, and then spraying the iodine complexing solution over the previously dried or partially dried insolubilized PVA treated surface overall, or selectively using masks etc. to form localized PVA iodine complexed patterns. The overall surface is PVA coated, but only selected areas of the PVA are thus complexed to form a black pattern.
This spraying method could reduce the rinsing steps for removal of excess iodine because little excess iodine would be sprayed. Since the PVA/iodine complex is black, the complexed PVA will be patterned a vivid black, especially when applied to a contrasting light colored sponge or other base substrates.
Another process that can apply the PVA/iodine complex selectively is by roller coat printing various patterns and concentrations of PVA resin solution onto the base sponge surface. The PVA pattern is dried/cured in a production line, and either overall sprayed, dipped, or like roller coat printed with an iodine solution, flushing out excess iodine and thus forming a patterned PVA/iodine complex as these uncoated areas having neither the PVA or iodine would be devoid of the black coloration.
Other antimicrobial components can be incorporated into the PVA/iodine solutions to accomplish initial greater antimicrobial effectiveness if these antimicrobial adjuncts were more water soluble than the PVA/iodine complex. Povidone iodine is an example of a well known water soluble antimicrobial that would be compatible with the iodine complexing solution to give quicker antimicrobial action. However, this water soluble component would only be useful if an iodine residue were acceptable.
The present invention also provides for mixing the PVA with other iodine complexing materials that are also compatible with PVA and/or iodine. These additives may increase the release rate and immediate concentration of iodine in the infected environment and be especially helpful in occurrences where large bacterial content is present, and quick effectiveness is necessary. Also, additives may be incorporated to reduce the iodine release rate by forming stronger iodine complexes than with PVA, useful where bacteria populations are smaller, and a longer lived antimicrobial environment is desirable. Applying the iodine complexing solution containing the more water soluble polyvinyl pyrolidone is an example of the former application, starch and starch derivatives such as cyclodextrin halide encapsulates mixed with the PVA is an example of the latter modification. The starches preferably would be used only with inanimate contact surfaces, as starches are generally not biocompatible in certain wound sites. Other antiseptic iodine compounds can be admixed with the PVA to counter various bacterial challenges.
Active PVA iodine complexes are characterized by having a deep blue black color (thinner coatings are light brown or blue) but when the iodine content is dissipating, the blue black color slowly fades away and the substrate""s color finally becomes the dominant color, e.g. if the substrate were white, the substrate then turns from black fading to blue or light brown to finally pure white or colorless indicating unmistakable activity, and as an indicator for replacement. This clearly evident color change is very convenient, especially for wound dressings, where decision for changing is made only after time consuming removal and examination. If a clear window film in the dressing showing the color of the dressing is present, this would avoid unnecessary changings. Furthermore, if the color was recently dissipated, there is no immediate need to replace the dressing, as the iodine complex causes a clean environment, for some time after, that inhibits bacterial growth. It is also obvious that this intrinsic property of dramatically changing color on iodine dissipation in dressing may also be a very important benefit for the users of wipers made by this invention. The form and composition of the substrate typically may be household type cellulose or urethane type sink sponges, washcloths, cheesecloth pads, gauze woven or non-woven rayons, papers and polyester non-woven materials, etc. These antimicrobial coated sponges, wipes and cloths are then useful as topically applied cleansing and sanitizing devices, e.g. scrubbers for use in industrial food handling and general sanitizing. Household sanitation, personal hygiene, wound healing dressings, clean room wipes, medical devices, antimicrobial coatings, are some other applications, all whose color change indicator of activity and longevity is critical for effectiveness.
A major advantage of PVA/iodine complexes is that they leave little or no detectable residues on their contacted surfaces. Other antimicrobial wipes, e.g. containing quaternary amines, alcohols, chlorinated cleansers, etc. all leave residues behind that may be toxic or create all organic reactions.
From the above discussions, it is evident that the present invention, in contrast to the prior art, allows the iodine content of the sponge to be a separate and independent consideration from the type and size of the sponge substrate, and does not require acetalized PVA foam to accomplish the complexing of the iodine with a sponge matrix. Sponge matrixes of many types are commercially available that would lend themselves as coating substrates for PVA iodine complexes, e.g. cellulose sponges which are composed of reconstituted cellulose mixed with fibers to give them strength and capillarity. These sponges are commonly used in households because they are inexpensive, absorbent, and relatively strong. They would readily absorb the PVA impregnate solution as the chemical properties of cellulose are similar to PVA, and the bonding of PVA to cellulose would be good. In fact, the PVA should improve the wet strength of the cellulose sponge and bind any loose fibers to reduce linting. Also, since cellulose sponges"" dry state is more flexible than PVA sponge when dry, the dry flexibility of the PVA coated cellulose sponge combination is better than PVA sponge alone, especially when thinner PVA coatings are applied. In addition, the fiber content of the cellulose sponge should improve the capillarity of the coated combination and improve the wicking rate compared to dry PVA sponge, and thereby reduce wet out times.
Cellulose sponges are available in many colors, thicknesses and pore size, shapes and embossments. Cellulose sink sponges during normal use act as a microbial culturing environment as cellulose is a nutrient for bacteria as well as the ever present particles of food, which results in an infection of the sponge, possible spread of bacteria, odors in the sponge and its degradation. Iodine prevents the proliferation of bacteria and therefore prevents all of the above.
PVA resins and starches are also especially noted for their sizing properties, useful in the paper, adhesive and weaving industries. PVA resins are used to coat many types of fibers, bonding well to their surfaces to aid in their processing, and PVA suppliers make special grades of PVA to fulfill these needs. These specialty grades of PVA can be adapted to coat many types of fibrous and porous matrixes, e.g. polyesters, metal screens, fiberglass, and urethane foam filters, non-woven cloths, and woven cloths, and when cured, give all these base matrixes iodine complexing potential to produce, e.g. antimicrobial versions of water filters, antifungal and antimicrobial substrates in air conditioning systems. (Legionnaire""s Disease was due to the lack of proper disinfection of the air conditioning system). In addition, these specialty grades of PVA, some of which are not best suitable for making PVA sponge, may yield unusual complexes with iodine due to their different degrees of insolubility of their iodine complexes. For example, partially hydrolyzed grades of PVA which contain acetate groups have more water solubility at room temperature than fully hydrolyzed grades, and produce complexes with varying iodine complexing properties. Thereby, mixes of different PVA grades could yield special antimicrobial effectiveness at different exposure times.
Open celled polyether polyurethanes and polyester urethane foams can be impregnated with various grades, molecular weights and concentrations of PVA, to be subsequently complexed with iodine to produce all kinds of antimicrobial sponges. Urethanes with 20-50 pores per inch are best suited for coating with PVA. Inexpensive and disposable products made of combinations of diverse matrixes can be developed by laminating, mixing fibers or otherwise bonding different matrixes. For example, combining a layer of cellulose base sponge to be subsequently iodine complexed with a more abrasive polyurethane sponge, or an abrasive containing polyester pad scrubber, the scrubber portion uncomplexed, will produce a multi-duty performing antimicrobial scrubber and polisher biofilm remover, and disinfectant.
PVA resin provides a much improved wet strength to an absorbent paper substrate while still maintaining some of the paper""s hydrophilic and absorbent properties. The paper will also have the typical desirable antimicrobial properties when coated lightly with PVA and subsequently iodine complexed. The PVA thereby performs the double function of supplying wet strength to cellulose pulp and papers and the medium for complexing with iodine. A further benefit that PVA provides to fibrous matrixes is that its excellent coating and adhesive characteristic allows it to bond well to fibers, causing the fibers to be more firmly attached to itself in the yam, thus forming a stronger, smoother sized matrix, reducing linting, and providing a less adhering, still absorbent, surface. Such a matrix, e.g. coffon gauze, felts, pads, or non-wovens, treated with PVA and iodine produces an excellent all in one antimicrobial non-adhering wound dressing. Another product that can be derived from this technology is a consumer single use personal wipe, e.g. a non-woven antimicrobial Wash and Dry type moist paper towelette or napkin in a traditional moisture retaining foil packet. This disposable product can be carried by the consumer to sanitize suspected eating utensils, telephone mouthpieces, push buttons, bathroom knobs and surfaces, surfaces that are expected to be contacted by a child, and other public handles. These specially sized wipes can be used oncexe2x80x94larger, multi-use wipe or wipes with different iodine contents may come in a resealable poly pouch. Surgical masks can be improved by having additional antimicrobial properties with the insertion of a tab of PVA iodine complex coated porous paper in the filtering layers. PVA/iodine antimicrobial activity segments can also be put on surgical drapes and gowns to make them more antiseptic by applying complexed labels, printing or otherwise applying the iodine complex to an insolubilized PVA coating. Areas of the drapes which would benefit most by having an antimicrobial environment would be those surrounding the incision site opening, as well as on the cuffs of the disposable surgical gowns. Insolubilized PVA forms more stable complexes with iodine than uncured PVA, as in the prior art. A more stable complex is defined as having the capability of complexing with more iodine, and retaining it over a longer period of time.